This invention relates to a semiconductor process, particularly relates to a method for growing a barium titanate layer by means of liquid phase deposition (LPD).
During the development of integrated circuits (ICs), the shrinkage of the device size can directly enhance the element density and reduce the delivery time of data. Consequently, the function and the application of the products will be widely enlarged. Thus, narrowing down the designing size of the device is always the devoted objective in IC industries. The IC has developed from LSI into ULSI in the past 20 years, wherein the DRAM is one of the important IC products.
In current IC process, silicon dioxide is the primary dielectric material used in the DRAM capacitor. With the increasing of the memory density of DRAM and the shrinking surface area of the memory cell, the thickness of the silicon dioxide used as the dielectric layer of the capacitor is reduced from 1000 xc3x85 to 100 xc3x85. Considering the development tendency, the thickness of silicon dioxide will be reduced to 35 xc3x85 soon, however the dielectric constant of the silicon dioxide with a thickness of 35 xc3x85 reaches only 3.9, which can not satisfy the requirement of advanced IC industries. Since it is necessary to provide enough charge storage capacity within a desired device area to remain the ability of signal processing. Therefore, it""s hard to further enhance the charge storage capacity by using the conventional silicon dioxide with low dielectric constant as the dielectric layer of the capacitor.
Therefore, it is urgent to develop a dielectric material with high dielectric constant, low leakage current and breakdown resistant, used as the dielectric layer of the capacitor to satisfy the requirement of the DRAM memory with the properties of high memory density and high charge storage within the limiting area.
BaTiO3 has properties of high dielectric constant (about 22.3), low leakage current (about 9.48xc3x9710xe2x88x927 A/cm2) and breakdown resistant; therefore, BaTiO3 is suitable to be the dielectric layer of the DRAM capacitor. So far, the deposition methods for BaTiO3 include Sol-gel, CVD and sputtering. Although Sol-gel proceeds at a low temperature, it needs a post high temperature treatment, however the wafer will deform and the doped impurities therein will re-distribute after annealing. According, the structure of devices will be damaged. Moreover, the drawback of CVD is the requirement of expensive apparatuses and proceeding at high-temperature (400xcx9c800xc2x0 C.). Although, sputtering is a low-temperature growing method, but the damage caused by the radiation emitted during the sputtering process is unavoidable. In brief, these three methods for growing the BaTiO3 layer exist various drawbacks when used to grow the BaTiO3 layer.
On the other hand, the apparatuses for liquid phase deposition (LPD) are cheap, and the growth temperature is low (ranging from 25xc2x0 C. to 80xc2x0 C.). Moreover, the process of LPD is easily to practice, and the thermal effect produced during growth is avoidable. Consequently, the cost for deposition can be highly reduced. According, this invention discloses a novel method for growing the BaTiO3 layer by means of LPD to satisfy the requirement of advanced IC products.
This invention disclose a method for growing a barium titanate layer by means of liquid phase deposition (LPD), which characterizes by low cost, low-temperature growth, and easily practice. This novel method for growing a barium titanate characterizes by mixing a barium nitrate solution and hexafluorotitanic acid solution to produce a barium titanate solution. Next, a boric acid solution is added to the barium titanate solution to prepare a barium titanate growth solution. Then a substrate, such as a wafer, ready to grow a bariumtitanate layer thereon is dipped in this growth solution for a period at a suitable temperature. Thereafter, a barium titanate dielectric layer with the properties of high dielectric constant, low leakage current and breakdown resistant can be formed on the substrate.